It is well known that centrifuges can be used to separate mixtures consisting of liquids of different densities and mixtures consisting of liquids and solids. Although there are a number of different designs for different applications, generally a centrifuge has at least one well that rotates about a central point. The well is held at a fixed diameter from the center and centripetal force prevents it flying off tangentially from its circular path. More commonly, when describing what a centrifuge does, people refer to the apparent centrifugal force which seems to push the well and its contents out from the central point when viewed in a rotating frame of reference.
This radial acceleration results in the more dense fraction settling at the point of the well most distal from the central point, and less dense fraction being located proximal to the central point. The acceleration rate and the duration of acceleration can determine what materials settle to the distal point. For example, a certain radial acceleration and duration will separate platelets from plasma, while another will separate cream from milk, and multiple-step centrifugation can separate DNA from lysed cells.
Among other uses, animal processors may use a centrifuge to separate water from solid materials, separate fats, collect gelatin, or to clean waste water.
The amount of material that can be processed in a centrifuge per unit of time is determined, in part, by the materials being separated, the radial acceleration rate, and the volume of the centrifuge wells. For most industrial applications, the materials being separated will be consistent and the radial acceleration rate will have been optimized for it. The volume of the wells is then of great importance. In use, the mixed materials are placed in the well and spun at the appropriate rate and time to achieve the desired separation. The centrifuge then spins down to a stop, the top fraction on top is poured off (or collected if needed), and the material at the bottom is removed. In animal processing and other applications in which the centrifuge is used to separate liquids from solids, some centrifuge designs decrease the need to stop the machine for material removal by using a liquid-material removal means such as pores in the well, tipping methods, or an aspiration means. Such liquid-material removal means allow the the addition of new mixed material while the centrifuge is spinning; and since the liquid material is removed during rotation, the centrifuge doesn't need to be stopped until the well is sufficiently full of the more dense material. However, when the well is full, the centrifuge needs to be brought to a stop and each well needs to be emptied before it can be started again.